Question: Solve for $z$ : $-20 = z - 4$
Answer: Add $4$ to both sides: $ \begin{eqnarray} \\ \hphantom{-20 {+ 4}} &\hphantom{=}& \hphantom{z} \\ -20 &=& z - 4 \\ \\ {+4} && {+4} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -20 {+ 4} &=& z \\ \end{eqnarray} $ Simplify. $ z = -16$